Air cells are power supplies which are economical because the cells use oxygen in the air as an active material and can be used for a long period of time without maintenance. As the conventional air cells, button-type air cells are known. A button-type air cell uses a casing assembly in which a metallic negative electrode casing and a metallic positive electrode casing having air holes are fitted to each other with a gasket interposed therebetween. Within the casing assembly, a negative electrode, an electrolysis solution, a separator, an air electrode (a positive electrode), a water-repellent film, and the like are arranged.
In the button-type air cell as described above, the internal space of the casing assembly is divided by the separator. One of the divided spaces is filled with zinc and electrolysis solution, in which zinc is immersed, to serve as the negative electrode, and the other space includes a catalyst to serve as the air electrode (the positive electrode). The water-repellent film is composed of porous membrane made of polytetrafluoroethylene (PTFE) and is provided on the surface of the air electrode opposite to the separator. Diffusion paper is tightly attached to the water-repellent film.
In the button-type air cell, oxygen in the air as a positive electrode active material is introduced through the air holes provided in the bottom of the positive electrode casing and is supplied to the air electrode through the diffusion paper and water-repellent film. In this configuration, the diffusion paper serves a function of uniformly supplying oxygen to the entire surface of the air electrode. The water-repellent film serves a function of supplying oxygen to the inside of the cell (the positive electrode) and a function of preventing the electrolysis solution from leaking out of the cell through the air holes.
Among the air cells configured as described above, there is a known air cell in which a catalyst layer is provided on a gas diffusion layer and a current collector is eccentrically located in the gas diffusion layer side of the catalyst layer (see Patent Literature 1, for example). This air cell further includes an air electrode shaped in a truncated cone decreasing in diameter in the direction from the gas diffusion layer to the top surface of the catalyst layer. This button-type air cell can prevent chunks of catalyst produced by collapse of the catalyst layer from entering gaps between constituent parts as foreign objects and is therefore excellent in liquid leakage resistance.